Experiments are in progress to identify a recombinant DNA containing Drosophila actin gene sequences by hybridization with the cloned yeast and Dictyostelium actin genes. The Drosophila actin gene hybrid will be characterized by in vitro translation of rescued RNA and by hybrid-arrest translation experiments. The number of actin genes present in Drosophila genome will be estimated from Southern transfer experiments and in situ hybridization to polytene chromosomes. Sites active in transcription will be identified by hybridization of actin gene sequences to nascent RNA on polytene chromosomes. The aim of this project is to study transcriptional control of a family of related genes during development.